24-Bit, Pin-Programmable, Ultralow Power Sigma-Delta ADC AD7780 FEATURES FUNCTIONAL BLOCK DIAGRAM GND AV GAIN REFIN(+) REFIN() DD Pin-programmable filter response Update rate: 10 Hz or 16.7 Hz AIN(+) DOUT/RDY Pin-programmable in-amp gain G = 1 24-BIT - OR 128 ADC Pin-programmable power-down and reset AIN() SCLK Status function DV DD BPDSW INTERNAL Internal clock oscillator CLOCK FILTER Internal bridge power-down switch AD7780 PDRST Current Figure 1. 115 A typical (gain = 1) 330 A typical (gain = 128) Table 1. Simultaneous 50 Hz/60 Hz rejection Parameter Gain = 128 Gain = 1 Power supply: 2.7 V to 5.25 V Output Data Rate 10 Hz 16.7 Hz 10 Hz 16.7 Hz 40C to +105C temperature range RMS Noise 44 nV 65 nV 2.4 V 2.7 V Independent interface power supply P-P Resolution 17.6 17.1 18.8 18.7 Packages Settling Time 300 ms 120 ms 300 ms 120 ms 14-lead, narrow body SOIC 16-lead TSSOP 2-wire serial interface (read-only device) SPI compatible Schmitt trigger on SCLK APPLICATIONS Weigh scales Pressure measurement Industrial process control Portable instrumentation GENERAL DESCRIPTION The on-chip PGA has a gain of 1 or 128, supporting a full-scale The AD7780 is a complete low power front-end solution for differential input of 5 V or 39 mV. The device has two filter bridge sensor products, including weigh scales, strain gages, and response options. The filter response at the 16.7 Hz update rate pressure sensors. It contains a precision, low power, 24-bit sigma- provides superior dynamic performance. The settling time is delta (-) ADC an on-chip, low noise programmable gain 120 ms at this update rate. At the 10 Hz update rate, the filter amplifier (PGA) and an on-chip oscillator. response provides greater than 45 dB of stop-band attenuation. Consuming only 330 A, the AD7780 is particularly suitable for In load cell applications, this stop-band rejection is useful to reject portable or battery-operated products where very low power is low frequency mechanical vibrations of the load cell. The settling required. The AD7780 also has a power-down mode that allows time is 300 ms at this update rate. Simultaneous 50 Hz/60 Hz the user to switch off the power to the bridge sensor and power rejection occurs at both the 10 Hz and 16.7 Hz update rates. down the AD7780 when not converting, thus increasing the The AD7780 operates with a power supply from 2.7 V to 5.25 V. battery life of the product. It is available in a narrow body, 14-lead SOIC package and a 16-lead For ease of use, all the features of the AD7780 are controlled by TSSOP package. dedicated pins. Each time a data read occurs, eight status bits are appended to the 24-bit conversion. These status bits contain a pattern sequence that can be used to confirm the validity of the serial transfer. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 07945-001AD7780 TABLE OF CONTENTS Features .............................................................................................. 1 Power-Down/Reset (PDRST) ................................................... 12 Applications ....................................................................................... 1 Analog Input Channel ............................................................... 12 Functional Block Diagram .............................................................. 1 Bipolar Configuration ................................................................ 12 General Description ......................................................................... 1 Data Output Coding .................................................................. 12 Revision History ............................................................................... 2 Reference ..................................................................................... 12 Specif icat ions ..................................................................................... 3 Bridge Power-Down Switch ...................................................... 13 Timing Characteristics ................................................................ 5 Digital Interface .......................................................................... 13 Absolute Maximum Ratings ............................................................ 6 Applications Information .............................................................. 14 Thermal Resistance ...................................................................... 6 Weigh Scales ................................................................................ 14 ESD Caution .................................................................................. 6 Performance in a Weigh Scale System ..................................... 14 Pin Configurations and Function Descriptions ........................... 7 EMI Recommendations ............................................................. 14 Typical Performance Characteristics ............................................. 8 Grounding and Layout .............................................................. 15 Output Noise and Resolution........................................................ 10 Outline Dimensions ....................................................................... 16 Theory of Operation ...................................................................... 11 Ordering Guide .......................................................................... 16 Filter, Data Rate, and Settling Time ......................................... 11 Gain .............................................................................................. 12 REVISION HISTORY 9/09Rev. 0 to Rev. A Changes to Specifications Table ...................................................... 3 4/09Revision 0: Initial Version Rev. A Page 2 of 16